In recent years, the scope of drug delivery technologies has expanded significantly, irrespective of the route of administration, as a result of an advanced understanding of disease, science, and safety associated with pharmaceuticals. The overall purpose of drug delivery systems, however, has remained constant: to provide a therapeutically effective amount of drug to the appropriate site in the body for a desired duration of action. The site at which a drug is delivered (drug targeting) and the rate at which the drug is released (profile) have to be carefully considered during dosage form design and product development. Sitespecific drug delivery has been one of the key focus areas for pharmaceutical formulation scientists for many decades.
The main purpose of site-specific drug delivery systems is to improve the efficacy and safety of drugs. Pharmaceutical scientists have also focused on the development of formulations that deliver drugs at a desired release rate, the duration of which may span from very fast (a few seconds) to very slow and controlled (days, weeks, and months). Combining site-specific aspects of drug delivery with controlled release rates is highly desirable for patient treatment.
For conventional oral dosage forms, the drug (active pharmaceutical ingredient [API]) is rapidly released after administration and subsequently absorbed into the body from the GI tract. The concentration of drug in the blood peaks shortly after administration as the drug absorption process dominates, then decreases over time as metabolism and/or excretion processes dominate. Conventional immediate-release (IR) dosage forms, however, do not maintain the plasma levels of the drug within the therapeutic range for an extended period of time and thus a short duration of action may be observed.
For many drugs and therapeutic indications, multiple dosing of IR formulations provides satisfactory clinical performance with an appropriate balance of efficacy and safety. For example, multidose therapy may be tolerated for short-term treatment, but is not desirable for treating chronic conditions. To reduce dosing frequency and eliminate the fluctuations in blood concentration associated with conventional delivery, extended-release (ER) systems have been and continue to be developed, where the drug is slowly released over an extended timeframe.
Delayed-release (DR) technologies exhibit a lag time in drug release (no drug released immediately) to target the drug to a specific site in the body. Both ER and DR systems are broadly referred to as modified-release (MR) dosage forms. The common goal for the development of any MR formulation is to enhance the drug’s therapeutic benefits, minimize side-effects, and improve the overall management of the disease. These technologies may be combined with conventional IR delivery or combined with other MR technologies.